'73 Jeep, 360 Wagoneer engine, probably a 60 amp alt. This thing has been chewed up and spit out many times since new, and little original wiring is in place, except the giant rat’s nest over my feet.
I hooked up a double battery system with an isolator, so there is just one wire going from the alt to the isolator. Some kind of diode or something that prevents “back drain”. Also have a marine dual battery switch and shutoff, but enough about my problems…
On-line searches show just running the gauge in-line on the wire that charges the battery. Is it really that easy? Will that gauge handle that amperage? (it goes up to 60 amps) It seems to good to be true that it would be that easy. I have a 100 amp gauge that the needle broke off, and it has a jumper between the two poles. Is that needed? The 60 amp gauge does not have that, but it would fit. I’m aware I’ll need to prevent shorts behind the dash (all custom made at this point).
I’ll use a 10-guage wire, heavily insulated where it passes thru the firewall.
Am I on the right track? It would be trivially easy to test, but want some advice before setting the Jeep on fire or wrecking the very cool ammeter I have.
10 guage would handle it but I believe 8 would be better, we ran them on all of our trucks years ago and we were using 6 guage. I don’t find much use for ampmeters if you know the voltage in the system. If you are running over about 13.6 you have more than sufficent amperage and all you need for a volt meter is a good +12 volt source.
Yeah, I actually agree with you on this. I have a real good voltage gauge, but the custom dash needed an extra gauge for “balance” and the ammeter is sooooo cool looking.
So, just wire it up “in-line” and everything is good to go? No better “come off the ignition wire at a lower amperage” solution? Or is that the voltage gauge I already have that works tits? I guess I’ll take the gauge with the broken needle and jump under the hood in-line and see what happens…
a true ammeter - the current must pass through the ammeter … it would have really big electrodes to carry 60 Amps…
an external shunt ammeter… well the device at the dashboard is a volt meter - the external shunt down at the battery is a resister.
Say 1 milli Ohm, showing 1 milliV per amp… Just change the volt meter’s label from mV to A…
I’ve got 3 gauges, two of them measure from 0-60 and the one with the jumper (and broken needle!) measures 0-100. All are only two pole, one in, one out. All are marked “+” on one pole, so not too ambiguous there. The one I intend on using is a vintage Stewart-Warner, out of an old Volvo, if memory stands correct. Standard 2" gauge, light with case/body ground, only two poles, insulated from each other. The pinch clamp is insulated also to prevent the poles from touching or touching the mounting point.
Not being an electrical type guy, I’m wondering, is that jumper allowing the bulk of the electrical charge to bypass the actual gauge but still read the amperage? I recall from a job at a speaker manufacturer a discussion about coils and such that would divert current and do things not intuitive to the layman. Hey, I did Accounts Payable, not engineering.
A auto ammeter is just a sensitive voltage sensor that measures the voltage difference between the alternator and the battery. As such it is not required to pass the total current through it, actually you can not, it is far too small, but only needs a small wire from both sources.
Unless this is something else entirely then the stock ammeter I has that plugged into the PCB of the dash panel, which after the connector failed on the PCB I rewired it direct as I just described. My ammeter didn’t use amps but C and D (Charge and Discharge)
It seems very impractical and perhaps potentially hazardous to run 6 gauge wire through the firewall.
And as stated, while the ammeter is cool, a voltmeter for a car is more practical.
Yep, this is how it’s been on the few cars I’ve owned with ammeters: the wire between the battery and alternator is used as a resistor shunt, and the voltage is measured between each end of the wire. Ohm’s Law, and all that stuff.
Because the wire between the battery and alternator is heavy gauge, its resistance is small, and thus there will only be a few millivolts between each end of the wire. But this is not a problem to measure.
The thing about automotive ammeters is that they’re usually just a dumb, cheap, analog gauge without numbers, and it doesn’t give you much of a feel for what’s going on. The best thing to have is a digital voltmeter w/ 0.1 V resolution attached to the battery. When the engine isn’t running the voltage should be around 12.6 V. When the engine is running the voltage should be somewhere between 13.5 V and 14.5 V; the actual voltage will depend on temperature and the battery’s state of charge.
If the engine is running, and the battery voltage is still around 12.6 V (or less), then you know the alternator isn’t working. If the voltage is excessively high when the engine is running – like around 15.5 V or more – then the voltage regulator has bit the dust.
Going further in this, if your alternator is not working with only a ammeter all you will see is that you are discharging with no indication on how much reserve is left in the battery. The voltmeter will give you a indication of how much reserve is left which can give you a indication of how far you can go and when you have to pull over.
Say you’re driving along and the alternator craps out. To estimate the battery’s state of charge while you’re driving, turn off as many things as possible (lights, fans, stereo, etc.) and look at the battery voltage gauge.
Voltage → Approximate[sup]a[/sup] % Charge
12.65 V → 100%
12.45 V → 75%
12.24 V → 50%
12.06 V → 25%
11.89 V → 0%
At the very least you’ll want a gauge that can measure with a resolution of 0.1 V. A resolution of 0.01 V would be even better.
[sup]a[/sup][sub]It’s approximate because it depends on a number of things, like current (these numbers assume 0 A), temperature, age of battery, additives in the acid, phase of moon etc.[/sub]
I would shy away from this type. I installed “true” aftermarket ammeters in two vehicles, and in both cases they built up enough resistance that they eventually disabled the electrical system. In the first case I spent several hundred dollars having the problem diagnosed before I disconnected the leads from the ammeter and connected them together; fortunately, in the second case I remembered in time to save my bank account (and sanity).
If I ever go aftermarket again — and I’m toying with the idea — it’ll be a voltmeter fer sure.
Well, for an ammeter I guess there are a number of approaches:
A gauge where all the current goes through it. As noted above, this solution sucks for a number of reasons.
Use the heavy gauge wire between the battery and alternator as a current shunt, and measure the voltage across it. Certainly better than #1, but also not very accurate.
Similar to #2, except install a true current shut, and measure the voltage across the shunt. This would be more accurate than #2, but less efficient and more expensive.
Install a clamp-around ammeter w/ integral Hall effect sensor, along with a gauge. This would give you an accurate measurement of the current, but it would also be pretty damn expensive.
Thank You! I think I’ll go look up Ohm’s Law and hook this sucker up like you describe. NOT straight in-line!
I wasn’t real crazy about the idea of running a big, hot wire thru the firewall (twice!) of a vehicle that is only used in pretty nasty off-road situations. Of course, I’ve had this gauge in the Jeep for years without it being hooked up! Don’t know what my big hurry is now?
Don’t know what my big hurry is now? 